[doc] Refactor the online doc, simple the sidebar

[NeoZhangJianyu]

Refactor the online doc structure.

Hope this is the new base of online doc, so that more improvement/refactor could be handled based it.

The reviewer could create comments or update the branch directly.

Here is my updated online doc demo: http://tgl-gen12-tce.sh.intel.com:8000/latest/index.html. All update will be shown in this demo web site. Please compare with current online doc: https://opea-project.github.io/latest/index.html.

Update list:

• Update the structure of documents in online doc page. No any content is changed.

• Reduce the navigator depth to 2 in sidebar.

• Move GenAI* to first level directory: projects.

• Short the first level directory's' name

• Every first level directory has one entry page. All other pages in this directory should be linked in the entry page or sub linked pages.

• Add first level directory:

  1. Tutorial. Content comes from the docs/examples.
  2. Repo link of OPEA.

• Ignore some warnings which block online doc building.

• This refactor make some documents can't be navigated in online doc website. If we need these documents, we must update the Entry page or sub linked pages to add link to them. When add link of missed pages, please check if the content is duplicated.

• The building time of online doc is shorted from 2 mins to 10 seconds.

• Rm the tailed space of lines.